U.S. patent application number 12/100320 was filed with the patent office on 2008-10-16 for image forming apparatus and control method therefor.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Hiroshi MATSUMOTO, Naohisa NAGATA, Akinobu NISHIKATA, Ichiro SASAKI, Satoru YAMAMOTO.
Application Number | 20080253818 12/100320 |
Document ID | / |
Family ID | 39853844 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253818 |
Kind Code |
A1 |
SASAKI; Ichiro ; et
al. |
October 16, 2008 |
IMAGE FORMING APPARATUS AND CONTROL METHOD THEREFOR
Abstract
An image forming apparatus that can satisfy productivity at the
time of double-sided image formation without jamming due to a
collision of a succeeding sheet with a preceding sheet, and without
upsizing of the apparatus. The image forming apparatus performs a
sheet circulation transport for circulating and transporting a
sheet to an image forming unit to perform image formation on both a
first side and a second side of the sheet. The sheet is fed to the
image forming unit at a predetermined image formation start timing
for the first side image formation. The first side image-formed
sheet is reversed, and re-fed to the image forming unit for the
second side image formation while causing the first side
image-formed sheet to wait at least one of sheet waiting positions.
A full state where all the sheet waiting positions are full of the
first side image-formed sheets is detected. The sheet feeding unit
is controlled so that the number of sheets on which the sheet
circulation transport is performed is greater than the number of
the sheet waiting positions. When the full state detecting unit
detects the full state, the sheet re-feeding unit is controlled so
that a head sheet among the first side image-formed sheets waiting
at the sheet waiting positions is fed in advance of the
predetermined image formation start timing.
Inventors: |
SASAKI; Ichiro; (Toride-shi,
JP) ; NAGATA; Naohisa; (Moriya-shi, JP) ;
NISHIKATA; Akinobu; (Abiko-shi, JP) ; YAMAMOTO;
Satoru; (Abiko-shi, JP) ; MATSUMOTO; Hiroshi;
(Toride-shi, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
P.O. BOX 826
ASHBURN
VA
20146-0826
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
39853844 |
Appl. No.: |
12/100320 |
Filed: |
April 9, 2008 |
Current U.S.
Class: |
399/401 |
Current CPC
Class: |
G03G 2215/00599
20130101; G03G 15/238 20130101; G03G 2215/00603 20130101 |
Class at
Publication: |
399/401 |
International
Class: |
G03G 15/00 20060101
G03G015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2007 |
JP |
2007-102924 (PAT. |
Claims
1. An image forming apparatus having an image forming unit arranged
to form an image on a sheet, and performing a sheet circulation
transport for circulating and transporting the sheet to said image
forming unit to perform image formation on both a first side and a
second side of the sheet, comprising: a sheet feeding unit arranged
to feed the sheet to said image forming unit at a predetermined
image formation start timing for the first side image formation; a
sheet re-feeding unit arranged to reverse the first side
image-formed sheet, and re-feed the first side image-formed sheet
to said image forming unit for the second side image formation
while causing the first side image-formed sheet to wait at least
one of sheet waiting positions; a full state detecting unit
arranged to detect a full state where all the sheet waiting
positions are full of the first side image-formed sheets; and a
control device arranged to control said sheet feeding unit so that
the number of sheets on which the sheet circulation transport is
performed is greater than the number of the sheet waiting
positions, and, when said full state detecting unit detects the
full state, control said sheet re-feeding unit so that a head sheet
among the first side image-formed sheets waiting at the sheet
waiting positions is fed in advance of the predetermined image
formation start timing.
2. An image forming apparatus as claimed in claim 1, wherein said
control device is arranged to transport the head sheet fed in
advance of the predetermined image formation start timing to a
registration alignment position, and then temporarily stops the
head sheet.
3. A control method of an image forming apparatus having an image
forming unit arranged to form an image on a sheet, performing a
sheet circulation transport for circulating and transporting the
sheet to said image forming unit to perform image formation on both
a first side and a second side of the sheet, said image forming
apparatus comprising a sheet feeding unit arranged to feed the
sheet to said image forming unit at a predetermined image forming
start timing for the first face image formation; and a sheet
re-feeding unit arranged to reverse the first side image-formed
sheet, and re-feed the first side image-formed sheet to said image
forming unit for the second side image formation while causing the
first side image-formed sheet to wait at least one of sheet waiting
positions, said control method comprising the steps of: detecting a
full state where all the sheet waiting positions are full of the
first side image-formed sheets; and controlling said sheet feeding
unit so that the number of sheets on which the sheet circulation
transport is performed is greater than the number of the sheet
waiting positions, and, when said full state detecting unit detects
the full state, controlling said sheet re-feeding unit so that a
head sheet among the first side image-formed sheets waiting at the
sheet waiting positions is fed in advance of the predetermined
image formation start timing.
4. A control method of an image forming apparatus as claimed in
claim 3, wherein said control step comprises transporting the head
sheet fed in advance of the predetermined image formation start
timing to a registration alignment position, and then temporarily
stopping the head sheet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image forming apparatus,
such as copying machines, and a control method therefor.
[0003] 2. Description of the Related Art
[0004] Conventionally, when both sides of multiple documents are
copied by an analog image forming apparatus that does not have a
function of storing read original image information, the following
approach is adopted. That is to say, image formation on the back
side of a sheet is performed in such a way that a sheet with an
image formed on one side by an image forming unit is not discharged
outside the apparatus, but temporarily stacked on an intermediate
tray, and upon reading an original image associated with the back
side of the sheet, the sheet is re-fed to the image forming
unit.
[0005] In contrast to this, an image forming apparatus having a
function of storing the read original image can achieve a
through-pass double-sided copying function, which does not have to
stack the sheet with an image formed on one side, in double-sided
copying (see, e.g., Japanese Laid-Open Patent Publication (Kokai)
No. 2002-145535).
[0006] Next, the operation method of double-sided copying in the
through-pass double-sided copying type image forming apparatus will
be described with reference to FIG. 10.
[0007] FIG. 10 is a view schematically showing a configuration for
illustrating the operation method of double-sided copying in the
through-pass double-sided copying type image forming apparatus.
[0008] First, for example, an automatic document feeder feeds
sheets, and all pages of a predetermined number of documents are
read by a scanner, and stored in a storage unit (not shown). For
example, when the document is a double-sided document, both sides
are read, thereafter, images of a predetermined number of sheets,
for example, three sheets of odd-numbered pages (the first page,
the third page, and the fifth page) of a document are sequentially
read from the storage unit. Then, after copy is sequentially
performed on the front faces (first side) of the sheets, which are
sequentially fed from a sheet feeding unit 601 in an image forming
unit 602, three front faces copied sheets P-1, P-2 and P-3 are
reversed by a switchback unit 603. Subsequently, the sheets are
sequentially transported in a double-sided path 604 to the image
forming unit 602, and stopped in a first-to-last position
relationship (in a non-stacked state).
[0009] When a first image of an even-numbered page is formed on the
back face (second side) of the sheet, the first (head) sheet P-1
among the three sheets stopped within the double-sided path 604 is
re-fed to the image forming unit 602 (hereinafter, this sheet
re-feeding is referred to as the "double-sided sheet re-feeding").
Then, a toner image corresponding to the image of the second page
read from the storage unit is formed on the back side of the first
sheet P-1. At that time, the remaining two sheets P-2 and P-3 in
the double-sided path 604 sequentially go ahead to in preparation
for the double-sided sheet re-feeding.
[0010] Next, the fourth sheet is newly fed from the sheet feeding
unit 601 to have an original image of the seventh page formed on
the front face, and is transported to the rearmost of the
double-sided path 604 and stopped. Then, the second sheet P-2
stopped at the front end in the double-sided path 604 is fed to the
image forming unit 602 in a double-sided sheet re-feeding fashion,
and the original of the fourth page is copied on the back side
thereof. Subsequently, a fifth sheet is newly fed to the image
forming unit 602 from the sheet feeding unit 601, and the original
of the ninth page is copied on the front face thereof.
[0011] In this manner, when the through-pass double-sided copying
function is implemented, the double-sided path 604 is filled up
with the single-sided copied sheets, and then feeding of a new
sheet from the sheet feeding unit 601 and the double-sided sheet
re-feeding are alternately performed.
[0012] Meanwhile, in recent years, since color printers have become
widespread and its image quality has improved, the size of image
data has been increased; thus a model is being increased in which
compressed image data is accumulated in a hard disk drive
(hereinafter referred to as the "HDD"), and, before image formation
is performed, the image data is read from the HDD and decompressed.
Further, printers have emerged which need much time for image data
processing because functionality of the printers is expanded and an
original image is subjected to various types of image processing;
thus further time is needed for preparation of image data before
image formation is performed.
[0013] Above all, some image forming apparatuses using an
intermediate transfer body, for example, generate the timing of
sheet feeding from a sheet feeding unit based on the timing of the
start of image formation because the time required to form a toner
image is longer than the time required to feed and transport
sheets. In such apparatuses, since image formation must be started
before the timing of the start of double-sided sheet re-feeding,
the preparation time of image data must be within a predetermined
time period.
[0014] Under such circumstances, if a delay in the preparation time
of data of an image to be formed is caused due to delay in reading
the data from the HDD or the like, the double-sided sheet
re-feeding of the sheet P-1 stopped at the front end in the
double-sided path 604 is delayed. As a result, the number of sheets
that are circulating through the apparatus (the number of sheet
circulation pages) sometimes exceeds the number of positions where
single-sided copied sheets are stopped within the double-sided path
604 (the number of sheet stop positions). In such a case, there is
a problem that a malfunction such as jamming occurs due to a
collision of a later sheet with an earlier sheet.
[0015] For example, a case is assumed where, in a configuration in
which there are three sheet stop positions as shown in FIG. 10, the
number of the sheet circulation pages is seven. That is to say, a
case is assumed where the sheet feeding unit is controlled to
initially continuously feed four sheets (the first page, the third
page, the fifth page, and the seventh page) for first side copying
(see FIG. 7B described later). After a minimum time (see ST in FIG.
5 described later) required for a sheet to circulate through the
apparatus for first side copying and to be re-fed for second side
copying has elapsed, the sheet of the seventh page is fed from the
sheet feeding unit. Then, the head sheet (corresponding to P-1 in
FIG. 10) stopped at a stop position in the double-sided path 604 is
re-fed as a second page.
[0016] At that time, if the double-sided sheet feeding of the sheet
of the head second page is delayed, a full state is reached in
which the sheets are waiting at all the three stop positions within
the double-sided path 604. As a result, since there is no stop
position for the first side-copied sheet of the seventh page, the
sheet of the seventh page collides with a sheet waiting at the
rearmost stop position (corresponding to P-3 in FIG. 10).
[0017] Conventionally, in order to avoid such a malfunction, the
number of the sheet circulation pages X has been determined so as
not to exceed the number of he sheet stop positions Y (X=2Y-1).
That is to say, in the configuration example in FIG. 10 in which
there are three sheet stop positions, the number of the sheet
circulation pages has been controlled to be five, that is, the
sheet feeding unit has been controlled to initially continuously
feed three sheets (the first page, the third page, and the fifth
page) for first side image formation (see FIG. 7B described
later).
[0018] However, in such control, the number of the sheet
circulation pages cannot be increased, thus productivity is
adversely affected. Accordingly, in order to satisfy productivity,
a method of enhancing the speed of sheet transport and a method of
increasing sheet stop positions have been known, and, for example,
there is a method of controlling the speed of sheet transport by
sheet size (e.g., Japanese Laid-Open Patent Publication (Kokai) No.
2005-280897).
[0019] As described above, the method of enhancing the speed of
sheet transport in order to satisfy productivity needs an expensive
drive motor or the like, resulting in increase in cost. Further,
for the method of increasing sheet stop positions, there is a
problem that the apparatus is upsized.
SUMMARY OF THE INVENTION
[0020] The present invention provides an image forming apparatus
and a control method therefor that can satisfy productivity at the
time of double-sided image formation without jamming due to a
collision of a succeeding sheet with a preceding sheet, and without
upsizing of the apparatus.
[0021] In a first aspect of the invention, there is provided with
an image forming apparatus having an image forming unit arranged to
form an image on a sheet, and performing a sheet circulation
transport for circulating and transporting the sheet to the image
forming unit to perform image formation on both a first side and a
second side of the sheet, comprising: a sheet feeding unit arranged
to feed the sheet to the image forming unit at a predetermined
image formation start timing for the first side image formation; a
sheet re-feeding unit arranged to reverse the first side
image-formed sheet, and re-feed the first side image-formed sheet
to the image forming unit for the second side image formation while
causing the first side image-formed sheet to wait at least one of
sheet waiting positions; a full state detecting unit arranged to
detect a full state where all the sheet waiting positions are full
of the first side image-formed sheets; and a control device
arranged to control the sheet feeding unit so that the number of
sheets on which the sheet circulation transport is performed is
greater than the number of the sheet waiting positions, and, when
the full state detecting unit detects the full state, control the
sheet re-feeding unit so that a head sheet among the first side
image-formed sheets waiting at the sheet waiting positions is fed
in advance of the predetermined image formation start timing.
[0022] The control device can transport the head sheet fed in
advance of the predetermined image formation start timing to a
registration alignment position, and then temporarily stops the
head sheet.
[0023] In a second aspect of the invention, there is provided with
a control method of an image forming apparatus having an image
forming unit arranged to form an image on a sheet, performing a
sheet circulation transport for circulating and transporting the
sheet to the image forming unit to perform image formation on both
a first side and a second side of the sheet, the image forming
apparatus comprising a sheet feeding unit arranged to feed the
sheet to the image forming unit at a predetermined image forming
start timing for the first face image formation; and a sheet
re-feeding unit arranged to reverse the first side image-formed
sheet, and re-feed the first side image-formed sheet to the image
forming unit for the second side image formation while causing the
first side image-formed sheet to wait at least one of sheet waiting
positions, the control method comprising the steps of: detecting a
full state where all the sheet waiting positions are full of the
first side image-formed sheets; and controlling the sheet feeding
unit so that the number of sheets on which the sheet circulation
transport is performed is greater than the number of the sheet
waiting positions, and, when the full state detecting unit detects
the full state, controlling the sheet re-feeding unit so that a
head sheet among the first side image-formed sheets waiting at the
sheet waiting positions is fed in advance of the predetermined
image formation start timing.
[0024] The control step can comprise transporting the head sheet
fed in advance of the predetermined image formation start timing to
a registration alignment position, and then temporarily stopping
the head sheet.
[0025] According to the present invention, sheet circulation
transport can be performed while keeping the number of sheets
maximum. Further, even if a delay in the preparation of an image to
be formed is caused due to delay in reading from the HDD or the
like, control can be provided to prevent the sheet circulation
transport from being disturbed, and to prevent jamming or the like
from occurring due to a collision of a succeeding sheet with a
preceding sheet. This eliminates the need to upsize the apparatus
due to an increase in sheet waiting points, thus the productivity
at the time of double-sided image formation can be satisfied.
Furthermore, this eliminates the need to use an expensive drive
motor or the like due to enhancement of the speed of sheet
transport, thus cost can be reduced.
[0026] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 a cross-sectional view showing a configuration of an
image forming apparatus according to an embodiment of the present
invention.
[0028] FIG. 2 is a block diagram showing a configuration of a
control unit in the image forming apparatus of FIG. 1.
[0029] FIG. 3 is a block diagram showing the inner configuration
and the periphery of an image memory unit in FIG. 2.
[0030] FIG. 4 is a view useful in explaining a sheet transport path
of the image forming apparatus of FIG. 1.
[0031] FIG. 5 is a view showing the sequence of sheet transport
control processing at the time of double-sided copying performed by
the image forming apparatus of FIG. 1.
[0032] FIG. 6 is a table showing the number of he sheet circulation
pages in the image forming apparatus of FIG. 1.
[0033] FIGS. 7A to 7C are views useful in explaining sheet stop
positions in the image forming apparatus of FIG. 1.
[0034] FIG. 8 is a flowchart showing the sheet transport control
processing performed by the image forming apparatus of FIG. 1.
[0035] FIG. 9 is a view useful in explaining the sheet transport
control processing performed by the image forming apparatus of FIG.
1.
[0036] FIG. 10 is a view schematically showing a configuration for
illustrating the operation of double-sided copying in a
through-pass double-sided copying type image forming apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] Preferred embodiments of the present invention will be now
described in detail with reference to the drawings.
[0038] <Configuration of Image Forming Apparatus>
[0039] FIG. 1 a cross-sectional view showing a configuration of an
image forming apparatus according to an embodiment of the present
invention.
[0040] As shown in FIG. 1, the image information device has a first
chassis unit 1 and a second chassis unit 2, which constitute a main
body of the image forming apparatus. A photosensitive drum 3, a
developing device 4, an exposure unit 5, a hopper unit 6, a
transfer unit 7, an exhaust unit 8, a sheet feeding deck unit 9,
and a first belt transport unit 10 are disposed in the first
chassis unit 1.
[0041] The developing device 4 causes toner to adhere to a latent
image formed on the photosensitive drum 3 to render the image
visible. The exposure unit 5 exposes image information on the
photosensitive drum 3 to form a latent image, and the hopper unit 6
replenishes the developing device with toner. The transfer unit 7
transfers to a sheet (recording medium) the toner image rendered
visible on the photosensitive drum 3. The exhaust unit 8 uses a fan
(not shown) to exhaust air from the first chassis. The sheet
feeding deck unit 9 has a right deck 9a and a left deck 9b, each of
which feeds sheets, and the first belt transport unit 10 transports
the transferred sheet to the second chassis unit.
[0042] The second chassis unit 2 is provided with a second belt
transport unit 11, a first fixing unit 12, and an exhaust duct 13,
and further, with a transport path 14, a second fixing unit 15, a
sheet re-feeding transport path 16 (sheet re-feeding device), a
reversing path 17, a double-sided path 18, a waste toner bottle 19,
a sheet discharge path 20, and a bypass transport path 22.
[0043] The second belt transport unit 11 transports to the second
chassis unit 2 a sheet having thereon an not-yet-fixed image for
which toner image has been transferred on the side of the first
chassis unit 1. The first fixing unit 12 fixes onto the sheet, the
image on the sheet for which toner image has been transferred in
the first chassis unit 1. The exhaust duct 13 mainly exhausts heat
from the fixing unit in the second chassis unit 2. Further, the
transport path 14 is for linking the first fixing unit 12 and the
second fixing unit 15. The second fixing unit 15 is for performing
gross control to achieve the improvement of image quality.
[0044] The re-feeding transport path 16 is for guiding sheets to be
re-fed at the time of double-sided copying. The reversing path 17
is for reversing the sheets to be re-fed. The double-sided path 18
is for transporting the reversed sheets to the transfer unit 7. The
waste toner bottle 19 is for storing waste toner. The sheet
discharge path 20 is for discharging sheets in which image
formation is finished, outside the apparatus. The bypass transport
path 22 is for feeding the sheets, which have passed through the
first fixing unit 12, directly to the re-feeding transport path 16
or the sheet discharge path 20.
[0045] <Configuration of Control Unit>
[0046] FIG. 2 is a block diagram showing a configuration of a
control unit in the image forming apparatus of FIG. 1.
[0047] The control unit 100 is provided with a CPU 201 that
performs basic control of the image forming apparatus of FIG. 1. A
ROM 206 into which a control program is written, a work RAM 205 for
performing processing, and an input/output port 204 are connected
to the CPU 201 through address bases and data bases.
[0048] Some areas of the ROM 205 serve as a backup RAM where data
is not deleted even if a power source is turned off. A motor
controlled by the image forming apparatus, various loading devices
such as a clutch, and an input device to the image forming
apparatus such as a sensor, which senses the position of sheet, are
connected to the input/output port 204.
[0049] The CPU 201 sequentially controls input/output via the
input/output port 204 according to the contents of the control
program in the ROM 206, and performs image formation. An operating
unit 203 is also connected to the CPU 201, and the CPU 201 controls
a display device and a key input device, which are not shown, of
the operating unit 203. A user uses the key input device to
instruct the CPU 201 to switch between image formation operation
modes and between views, and the CPU 201 shows the operating state
of the image forming apparatus, and the operation mode that is set
by the key input, on the display device of the operating unit 203.
An image processing unit 170 for processing image signals and an
image memory unit 171 for accumulating processed images are also
connected to the CPU 201.
[0050] <Inner Configuration and Peripheral Devices of Image
Memory Unit 171>
[0051] FIG. 3 is a block diagram showing the inner configuration
and the peripheral devices of the image memory unit 171 in FIG.
2.
[0052] The image memory unit 171 is comprised of a page memory 401,
a memory controller unit 402, a compression/decompression unit 403
and a hard disk 404. Image data sent from an external I/F
processing unit 172 and the image processing unit 170 to the image
memory unit 171 is written into the page memory 401 by the memory
controller unit 402. Subsequently, the data is sent to a printer
unit 180 through the image processing unit 170, or accumulated in
the hard disk 404. When the image data is accumulated in the hard
disk 404, the image data is compressed by the
compression/decompression unit 403, and written into the hard disk
404 as compressed data.
[0053] The memory controller 402 also reads out to the page memory
401 the image data stored in the hard disk 404. At that time, the
compressed data read from the hard disk 404 is decompressed by the
compression/decompression unit 403, and the uncompressed image data
is written into the page memory 401. In addition, the memory
controller unit 402 generates DRAM refresh signals that are to be
sent to the page memory 401. The memory controller unit 402 also
conducts arbitration of the access from the external I/F processing
unit 172, the image processing unit 170 and the hard disk 404 to
the page memory 401. Further, according to instructions from the
CPU 201, the memory controller unit 402 determines and controls a
write address into the page memory 401, a read address from the
page memory 401, a readout direction and the like.
[0054] The above processing allows the CPU 201 to arrange and lay
out a plurality of original images in the page memory 401, and then
control a function of outputting the images to the printer unit 2
through the image processing unit 170. Further, the CPU 201 can
control a function of cutting only a portion of an image and
outputting it, and a function of rotating an image.
[0055] <Sheet Transport Control at the Time of Double-Sided
Copying>
[0056] The sheet transport control processing at the time of
double-sided copying, which is performed by the image forming
apparatus of FIG. 1, will now be described.
[0057] (A) Sheet Transport Control
[0058] FIG. 4 is a view useful in schematically explaining a sheet
transport path of the image forming apparatus of FIG. 1.
[0059] A sheet transport path system in the present embodiment is
comprised of roughly classified ten sheet transport paths. That is
to say, a right deck sheet feeding path 501, a left deck sheet
feeding path 502, a main transport path 503, a bypass transport
path 504 (reference numeral 22 in FIG. 1), a first fixing path 505
(reference numeral 14 in FIG. 1), and a straight sheet discharge
path 506 are disposed in the sheet transport path system. Further,
the sheet transport path system is provided with a reverse
discharge path 507 (reference numeral 17 in FIG. 1), a double-sided
reversing path 508, a double-sided transport path 509 (reference
numeral 18 in FIG. 1) and a double-sided sheet re-feeding path 510,
as a path used in double-sided copying.
[0060] The procedure of the sheet transport control processing at
the time of double-sided copying, which is performed by the image
forming apparatus of FIG. 1, will now be described.
[0061] First, based on the start of the formation of a latent image
for the first side of a sheet with respect to the photosensitive
drum 3, the sheet is fed from the right deck 9a after a
predetermined time has elapsed. Here, the predetermined time is a
difference between a time required for the sheet to travel from an
exposure position on the photosensitive drum 3 to the transfer unit
7 and a time required for the sheet transported by the sheet
feeding deck unit 9 to travel to the transfer unit 7 through the
main transport path 503. The right deck 9a and the left deck 9b
must be made different in the predetermined time from each other,
because they have different sheet transport path distances.
[0062] Next, after passing through the first fixing unit 12, the
sheet for which the toner image has been transferred is transported
to the straight sheet discharge path 506 through either of the
bypass transport path 504 or the first fixing path 505, depending
on the type of the sheet. The straight sheet discharge path 506 has
a path switching mechanism (not shown), by which first side-copied
sheets are transported to the reverse discharge path 507, and
second side-copied sheets are transported in such a direction that
the sheets are directly discharged outside the apparatus.
[0063] The first side-copied sheet transported to the reverse
discharge path 507 is reversed by the double-sided reversing path
508, and fed to the double-sided transport path 509. The
double-sided transport path 509 has a plurality of positions where
sheets can be stopped according to size (sheet stop position) so as
to control sheets to be transported to a stop position where there
is no preceding sheet. When a preceding sheet exists on a stop
position, the transport of the succeeding sheet is temporarily
stopped at the previous stop position. Subsequently, at the timing
at which the preceding sheet exits from the stop position, or at
the timing at which the preceding sheet is determined to exit from
the stop position, the transport of the succeeding sheet
temporarily stopped is restarted.
[0064] Based on the start of the formation of a latent image for
second side copying with respect to the photosensitive drum 3, the
double-sided sheet re-feeding operation is started after the
predetermined time has elapsed, and the sheet that reached the end
of the double-sided transport path 509 is transported to the
double-sided sheet re-feeding path 510. Thereafter, as described
above, after passing through a process in which a toner image is
transferred to the sheet, and a process in which the toner image is
fixed onto the sheet, the sheet is discharged outside the
apparatus.
[0065] The double-sided copying of the first side and the second
side is performed by continuously carrying out this series of sheet
transport alternating between the first side copying and the second
side copying.
[0066] FIG. 5 shows the sequence of sheet transport control
processing at the time of double-sided copying performed by the
image forming apparatus of FIG. 1.
[0067] FIG. 5 shows a five-page circulating sequence with the
number of sheet circulation pages of five, and a seven-page
circulating sequence with a sheet circulation page number of seven.
In the five-page circulating sequence, after three sheets for first
side copying (the first page, the third page, and the fifth page)
are initially continuously fed from the sheet fixing deck unit 9,
the first side copying and the second side copying are continuously
alternated. In the seven-page circulating sequence, after four
sheets for first side copying (the first page, the third page,
fifth page, and the seventh page) are initially continuously fed
from the sheet feeding deck unit 9, the first side copying and the
second side copying are continuously alternated. Note that ST shown
in FIG. 5 indicates a minimum time required for a first side-copied
sheet to circulate and to be fed for second side copying.
[0068] (B) The Number of Sheet Circulation Pages
[0069] FIG. 6 is a table showing the number of sheet circulation
pages in the image forming apparatus of FIG. 1.
[0070] In the example of FIG. 6, three types of sheet circulation
control are performed depending on sheet sizes. The sheet
circulation page number X is set in such a way that the
multiplication factor of the minimum time (ST in FIG. 5) required
for a first side-copied sheet to circulate and be fed for second
side copying, with respect to the time corresponding to
productivity determined by sheet size, is less than a minimum even
number N. That is to say, the relationship between N and X is as
follows:
X=N-1
[0071] (C) The Number of Relationship Between Sheet Circulation
Pages and the Number of Sheet Stop Positions
[0072] Next, the relationship between the sheet circulation page
number described above and the sheet stop position number will be
described with reference to FIGS. 7A to 7C.
[0073] FIGS. 7A to 7C are views useful in explaining sheet stop
positions in the image forming apparatus of FIG. 1.
[0074] As shown in FIG. 7, the relationship between the sheet
circulation page number and the sheet stop position number is as
follows:
[0075] the number of sheet circulation pages: 13.revreaction.the
number of sheet stop positions: 6 (a-1 to a-6 in FIG. 7A)
[0076] the number of sheet circulation pages: 7.revreaction.the
number of sheet stop positions: 3 (b-1 to b-3 in FIG. 7B)
[0077] the number of sheet circulation pages: 5.revreaction.the
number of sheet stop positions: 2 (c-1 and c-2 in FIG. 7C)
[0078] That is to say, the number of the sheet stop positions (that
is, the number of waiting sheets) Y and the number of the sheet
circulation pages X can be expressed as follows:
X=2Y+1
[0079] The number of waiting sheets Y is one sheet less than the
number of continuously feedable sheets for the first side-copied
sheets in FIG. 10. That is to say, in the present embodiment, the
number of sheet stop positions at the time of double-sided copying
can be reduced.
[0080] Also in the sheet transport control processing in such
(X=2Y+1), as described with reference to FIG. 5, sheets are
initially continuously fed for first side copying, and images are
formed, and, immediately after the ST time has elapsed, the head
sheet among the sheets that are waiting at sheet stop positions is
re-fed for second side copying. Thus, since some of sheet stop
positions become available, the next first side-copied sheet is fed
thereto.
[0081] At that time, if a delay in the preparation of data of an
image to be formed is caused due to delay in reading from the HDD
or the like, the double-sided sheet re-feeding of the head sheet
for second side copying would be delayed. Accordingly, this causes
a shortage of sheet stop positions, thus leading to a problem that
a malfunction such as jamming occurs due to a collision of a
succeeding sheet with a preceding sheet in the double-sided
reversing path 508.
[0082] According to the present embodiment, in order to avoid the
malfunction, the following control is performed. That is to say,
when it is detected (detection of full state) that all the sheet
stop positions are full of sheets (full state), the double-sided
sheet re-feeding of the head sheet waiting at the sheet stop
position is controlled to be performed in advance of the start of
image formation, which is originally the timing of feeding.
Hereinafter, such characteristic sheet transport control processing
of the present embodiment will be described in detail with
reference to FIGS. 8 and 9.
[0083] (D) Sheet Transport Control Processing
[0084] FIG. 8 is a flowchart showing the sheet transport control
processing performed by the image forming apparatus of FIG. 1. FIG.
9 is a view useful in explaining the sheet transport control
processing performed by the image forming apparatus of FIG. 1.
[0085] For ease of explanation, in the examples in FIGS. 8 and 9,
the seven-page circulating sequence with the number of sheet
circulation pages of seven (see FIG. 5) is performed in a
configuration in which there are three sheet stop positions as
shown in FIG. 9, for example. Further, the control is achieved in
such a way that a program code for sheet transport control stored
in the ROM 206 is read, and the CPU 201 performs the program
code.
[0086] Initially, it is determined whether or not the sheet stop
positions b-1 to b-3 are full (step S901). If the sheet stop
positions are not full at this point of time, the apparatus waits
until a predetermined timing for starting latent image formation
(step S902), on the other hand, if the sheet stop positions are
full, waits until a predetermined timing at which there is no
collision of sheets (step S910), and then the apparatus determines
again whether or not the sheet stop positions b-1 to b-3 are full
(step S911).
[0087] As a result of the determination of step S901, if the sheet
stop positions b-1 to b-3 are not full (NO to the step S901), when
latent image formation is started (NO to the step S902), the
apparatus starts double-sided sheet re-feeding after waiting until
double-sided sheet re-feeding timing (YES to the step S903), and
transports a sheet for second side copying (step S904).
[0088] Finally, synchronization is performed (hereinafter referred
to as the "registration alignment") so that the front end of the
sheet for second side copying for which transport has been started,
and the front end for a toner image which is formed from a latent
image are fed to the transfer unit 7 at the same timing (step
S905), followed by terminating the process.
[0089] As a result of the determination of step S911, if the sheet
stop positions are not full, processes from steps S902 to S905 are
performed as described above, followed by terminating the
process.
[0090] As a result of the determination of step S911, if the sheet
stop positions are full, the apparatus determines that the sheets
might collide at the sheet stop position b-3, and starts the
double-sided sheet re-feeding of the head sheet (the second page in
FIG. 5) waiting at the sheet stop position b-1 (step S912), without
waiting until the original double-sided sheet re-feeding timing
(after a predetermined time has elapsed from the start of latent
image formation). Thus, a waiting space for the subsequent first
side-copied sheet (the seventh page in FIG. 5) can be reserved.
[0091] Next, the sheet for which the double-sided sheet re-feeding
has been started earlier is transported to the predetermined
position b-4 on the main transport path 503 where the registration
alignment described above is performed, and the sheet is
temporarily stopped (step S913), and the start of latent image
formation is waited for (step S914). In this manner, the sheet for
which the double-sided sheet re-feeding has been started earlier is
temporarily stopped to carry out adjustment of the timing with the
latent image formation start timing (predetermined timing).
[0092] Finally, when the latent image formation is started (YES to
the step S914), the registration alignment is performed (step
S905), followed by terminating the process.
[0093] Note that in the present embodiment, the transport of the
sheets temporarily stopped at the later sheet stop positions b-2
and b-3 is restarted immediately after the double-sided sheet
re-feeding is started in the step S912, which is not shown in FIG.
8. Accordingly, this allows the double-sided reversing path 508,
which is the last sheet stop position b-3, to be available so as to
accept the last sheet for first side copying.
[0094] Further, in the present embodiment, the determination of
whether or not the sheet stop position is full is based on a
condition that a difference between the number of the fed first
side-copied sheets and the number of the sheets for second side
copying becomes zero. The similar determination can be performed by
other methods.
[0095] <Advantage of the Present Embodiment>
[0096] Conventionally, because of a problem in specific environment
such as delay in reading from the HDD or the like, the number of
the sheet circulation pages is reduced (X=2Y-1), thus productivity
is adversely affected; in contrast to this, in the present
embodiment, if the sheet stop positions b-1 to b-3 are full (YES to
the step S911), the apparatus does not wait until the double-sided
sheet re-feeding timing (skips the step S903), but starts the
double-sided sheet re-feeding (step S912), thus sheet transport
control can be performed while keeping the number of double-sided
sheet circulation pages maximum (X=2Y+1). Further, even if a delay
in the preparation of an image to be formed is caused due to delay
in reading from the HDD or the like, control can be provided to
prevent the sheet transport control from being disturbed, and to
prevent jamming or the like from occurring due to a collision of a
succeeding sheet with a preceding sheet. This eliminates the need
to upsize the apparatus due to an increase in sheet stop positions,
thus the productivity at the time of double-sided copying can be
satisfied. Furthermore, this eliminates the need to use an
expensive drive motor or the like due to enhancement of the speed
of sheet transport, thus cost can be reduced.
[0097] It is to be understood that the object of the present
invention may be accomplished by supplying a system or an apparatus
with a storage medium in which a program code of software which
realizes the functions of the above described embodiment is stored,
and causing a computer (or CPU or MPU) of the system or apparatus
to read out and execute the program code stored in the storage
medium.
[0098] In this case, the program code itself read from the storage
medium realizes the functions of any of the embodiments described
above, and hence the program code and the storage medium in which
the program code is stored constitute the present invention.
[0099] Examples of the storage medium for supplying the program
code include a floppy (registered trademark) disk, an HDD, a
magnetic-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a
DVD-RAM, a DVD-RW, a DVD+RW, a magnetic tape, a non-volatile memory
card, and a ROM. Alternatively, the program may be downloaded via a
network.
[0100] Further, it is to be understood that the functions of the
above described embodiment may be accomplished not only by
executing a program code read out by a computer, but also by
causing an OS (operating system) or the like which operates on the
computer to perform a part or all of the actual operations based on
instructions of the program code.
[0101] Further, it is to be understood that the functions of the
above described embodiment may be accomplished by writing a program
code read out from the storage medium into a memory provided on an
expansion board inserted into a computer or in an expansion unit
connected to the computer and then causing a CPU or the like
provided in the expansion board or the expansion unit to perform a
part or all of the accrual operations based on instructions of the
program code.
[0102] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications, equivalent
structures and functions.
[0103] This application claims priority from Japanese Patent
Application No. 2007-102924 filed Apr. 10, 2007, which is hereby
incorporated by reference herein in its entirety.
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